1. Field of the Invention
The present invention relates to a numerical controller that performs 3-dimensional interference check in relation to a variation in the feedrate so that collisions can be avoided properly.
2. Description of the Related Art
As an example of a numerical controller that drives and controls a movable part of a machine based on a command of a program, Japanese Patent Application Laid-Open No. 2008-27376 discloses a numerical controller which includes an interference checking unit that calculates the position (hereinafter referred to as a look-ahead position) of a movable part, a predetermined period after the current time, calculated based on a programmed speed and a programmed speed override value and checks an interference between the movable part and another object based on the look-ahead position and in which the movement of the movable part is decelerated and stopped when an interference is predicted by the interference checking unit.
When the technique disclosed in Japanese Patent Application Laid-Open No. 2008-27376 is to be used, a period (hereinafter referred to as a “look-ahead period”) from the current position to the look-ahead position, calculated by the numerical controller to allow the interference checking unit to predict an interference to safely decelerate and stop the movement of the movable part is set to a period that is not less than a value (=TP1+TP2+TP3+α) in which TP1 is the time required for the interference check, TP2 is the time required for communication between the interference checking unit and the main body of the numerical controller, TP3 is the time elapsed until the moving movable part is decelerated and stopped, and a is the time allowance.
The look-ahead period is a period in which the movable part can be safely stopped when the current feedrate is used as a reference. Thus, if the feedrate (override value) is changed by an operator, the interference may have already occurred when it is predicted by the interference check that the interference occurs. Thus, there is a problem that it is not possible to safely stop the movable part until a predetermined period elapses (from the time at which the feedrate is changed until interference check is completed based on the look-ahead position after the feedrate changes) even when it is predicted that the interference occurs.
FIG. 7 is a graph illustrating the relation between a current position of a movable part at time Tn and a look-ahead position used in interference check when controlling a single-path machine.
As illustrated in FIG. 7, when interference check at a look-ahead position PP(Tn) at a look-ahead period which is not less than TP1+TP2+TP3+α at each time Tn is completed at Tn+1, it is possible to stop the movement of the movable part safely in principle even after the occurrence of the interference is detected, so long as a coordinate value of a current position does not surpass a coordinate value P′P(Tn−1) of a look-ahead position at which interference check has already been completed.
FIG. 8 is a graph illustrating the relation between a current position of a movable part at time Tn and a look-ahead position used in interference check when an override is changed when controlling a single-path machine.
As illustrated in FIG. 8, when an override is changed at the time between T0 and T1, since a coordinate value of a current position surpasses a coordinate value of a look-ahead position at which interference check has already been completed as in portion (1) indicated by a bold line in the drawing, the interference check is not completed in the portion indicated by the bold line. Thus, there is a possibility that the movable part cannot be stopped safely.
FIGS. 9A to 11 illustrate an example in which an override is changed when controlling a multi-path machine.
When movable parts are operated without changing an override when controlling Path 1 illustrated in FIG. 9A and Path 2 illustrated in FIG. 9B, it is determined (interference check is completed) at time T2 (indicated by A in FIG. 10) that a look-ahead position of Path 1 and a look-ahead position of Path 2, which are subjected to interference check at time T1 interfere with each other as illustrated in FIG. 10. Thus, it is possible to safely stop the respective movable parts before the coordinate values of current positions of respective paths reach coordinate values at which the interference occurs. However, when an override of Path 1 is changed at time between T0 and T1, as shown in FIG. 11, the coordinate values of the current positions of the respective paths cross each other at the position indicated by B in FIG. 11 before interference check based on the look-ahead position of Path 1 and the look-ahead position of Path 2 at time T1 is completed. Thus, there is a possibility that the movable parts cannot be stopped safely.